1. Field of the Invention
The present invention generally relates to digital television technologies, and more particularly to a method and system for scanning a frequency channel in digital television.
2. Description of the Related Art
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
The technical advances have enabled the transmission of digital television (“DTV”) signals in the same bandwidth currently used by the analog National Television System Committee (“NTSC”) television system. DTV transmission employs digital modulation techniques, such as the eight-level vestigial sideband (“VSB”) modulation scheme developed by the Advanced Television Standards Committee (“ATSC”) in the United States, which utilize scarce bandwidth in a more spectrally efficient manner to transport and present audio and video signals. As a result, digital television allows more channels containing more information to be broadcasted within an equivalent bandwidth utilized by the current analog television system. To facilitate the reception of these numerous channels, certain DTV receivers are equipped with a channel auto-scanning function that automatically scans each channel to detect the presence of program content when such DTV receivers are turned on for the first time.
To illustrate, FIG. 1 is a simplified conceptual diagram showing how a conventional DTV receiver performs the channel auto-scanning function. Once the DTV receiver is turned on, a transmitted radio-frequency (“RF”) signal received via an antenna 102 is first tuned to a selected frequency channel and processed in a RF signal reception stage 104, through which the RF signal is converted to an intermediate frequency (“IF”) signal. The IF signal is then put through a synchronization stage 106 in which the carrier wave of the RF signal is recovered using a pilot tone embedded in the transmitted RF signal. Based on the recovered carrier wave, a baseband signal is demodulated and processed through an equalization stage 108 to remove any linear distortions, such as spectrum tilt and multi-path echo. The baseband signal is then processed in a phase tracking stage 110 that removes any remaining phase noise. After the output of the phase tracking stage 110, data packets that contain program identification codes are restored, which are used to detect the presence of program content in the selected frequency channel in a program content detection stage 112. The same procedure described above is repeated to operate on a next frequency channel in an attempt to detect the presence of program content.
While the aforementioned approach can detect the presence of program content, the amount of time required to complete the scanning procedure from the RF reception stage 104 through the program content detection stage 112 for all the different frequency channels is long. As the number of channels, especially for DTV, continues to grow (e.g., in excess of hundreds), the amount of time required to accomplish the channel auto-scanning function is also becoming unacceptably long.
What is needed in the art is thus a method and system that can cost effectively and efficiently scan a frequency channel to detect the presence of program content and address at least the problems set forth above.